Rolling element bearings are one of the most common and frequently failing components in rotating machinery. A rolling element bearing often includes the following four subcomponents: bearing balls, a cage, an outer race, and an inner race. The bearing balls typically move during rotation of a machinery element, and the cage typically helps to maintain separation of the balls. Each race is typically a grooved ring, and the bearing balls move between the races.
A crack, indentation, or wear in any one of these subcomponents often requires replacement of the entire rolling element bearing. Not only that, the failure of a rolling element bearing often causes immense secondary damage, such as shaft misalignment, rub, stator insulation failure, and gear failure. Therefore, the monitoring of the condition of a rolling element bearing is often an important activity in many industries.